Environmental factors in schizophrenia: the role of migrant studies.

There is now compelling evidence that migrant groups in several countries have an elevated risk of developing schizophrenia and other psychotic disorders. Though the findings of earlier studies were greeted with skepticism, and ascribed by some to have methodological shortcomings and diagnostic biases, the more rigorous recent studies, from a variety of countries, have still found markedly increased incidence rates. While this phenomenon is an important health issue in its own right, understanding the reasons for the increased rates may provide valuable insights into the causes of schizophrenia and other psychotic disorders in general. The challenge for the next phase of studies is to identify the relevant risk factors and how they might interact to increase the risk of psychosis, both in migrant groups and in the general population.